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At 01:34 AM 4/4/99 -0500, Bill Wolk wrote:
>
>Who knows? Buhlman's work has proved itself to be reliable for the most 
>part and (except for the helium algorithm) was well tested.  All the rest 
>is educated guesswork that may model decompression better in some ways 
>and less well in others. What amazes me about mix diving (and deco diving 
>in general) is that we're really flying by the seat of our pants.  
>Basically, what works is what works.  To me, that's a very sobering 
>thought. 

Bill, I heard (on the lists) and accepted for a while 
the information that Buhlmann's helium values were derived 
from nitrogen values and were untested.

However, I'm looking at Buhlmann's 'Decompression, Decompression 
Sickness' and it clearly states that (at least with the ZH-L12 
algorithm) a great number of experimental heliox dives were done 
with volunteer subjects. To quote Buhlmann "The persistent
reexamination and expansion of the original concept finally
yielded a method of decompression that is theoretically sound
and has been tested widely for nitrogen and helium."

Further, with regard to the experimental part of the research
programme, he wrote "With the concept developed in Zurich the 
simultaneous breathing of nitrogen and helium and the change from 
helium to nitrogen were fundamental; it was therefore always 
necessary in this research to consider both gasses."

And further, "Experiments were conducted with voluntary human
subjects but none with animals. The continuity of personnel
since the beginning made the consequent planning of experiments
easier. Tables 6, 7, 10 - 12 and 15  present information 
concerning hyperbaric exposures that were especially important 
for the the development of ZH-L12. With Oxygen and Helium as 
the breathing gas, exposures to saturation, experiments with 
fast compression, and exposures of only some minutes' duration 
at full pressure were executed up to a pressure of 50 bar."

The tables refered to above detail some 780 experimental dives,
mostly heliox or trimix with nitrox and/or oxygen decompression. 

Do you know from where we get the idea that Buhlmann's helium 
coefficients were derived and never tested? 


rgrds  billyw


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